Auxilliary reservoir for a liquid system

ABSTRACT

A liquid system for circulating a liquid through a circulation loop includes a liquid pump, a primary liquid reservoir and an auxiliary liquid reservoir. The liquid pump pressurizes liquid within the circulation loop. The primary liquid reservoir has a primary variable volume expandable to accommodate volumetric expansion of pressurized liquid up to a threshold volume. The auxiliary liquid reservoir has an auxiliary variable volume expandable only after the threshold volume is exceeded up to a maximum volume.

BACKGROUND

The present invention relates to liquid circulation systems and more particularly to reservoirs for liquid cooling systems used in aircraft.

Modern aircraft include many complex systems that include liquid circulation systems, such as environmental control systems, galley cooling systems and electronics systems. These systems are interconnected through a network that circulates various fluids and gases between the systems using components such as valves, pumps and electric motors. Some of these liquid systems generate heat that is carried away by other fluid systems to be dumped overboard from the aircraft. For example, the components are controlled by power electronics that consume large amounts of electric power and therefore generate heat that must be removed. Typical cooling systems used in these liquid systems involve closed loops that circulate a liquid coolant, such as a mixture of water and glycol, through heat exchangers using pumps.

The cooling systems are subject to temperature extremes ranging from the extreme cold of the upper atmosphere to the high temperatures generated within the systems. The liquid coolant therefore undergoes wide ranging temperature changes, which varies the volume of the liquid coolant due to thermal expansion. In order to absorb the volumetric expansion of the coolant throughout the operating cycle of the system, liquid cooling systems are provided with accumulators or reservoirs that provide an overflow volume. The reservoir holds a volume of coolant when temperatures are hot and the coolant is expanded. The reservoir returns the coolant to circulation when the coolant cools and contracts. In order to reduce the size of the cooling system and the space occupied in the aircraft, the reservoir is often incorporated into a package with the pump. For example, bootstrap reservoirs use pump inlet and outlet pressures to adjust the reservoir volume with system pressure changes. Furthermore, the capacity of the reservoir is typically sized for the requirements of a particular cooling system and aircraft platform. As such, redesign or scaling of pump-integrated accumulators is not a cost-effective option when designing liquid systems for new aircraft platforms.

SUMMARY

The present invention is directed to a liquid system for circulating a liquid through a circulation loop, such as liquid cooling loops used in aircraft. The liquid system comprises a liquid pump, a primary liquid reservoir and an auxiliary liquid reservoir. The liquid pump pressurizes liquid within the circulation loop. The primary liquid reservoir has a primary variable volume expandable to accommodate volumetric expansion of pressurized liquid up to a threshold volume. The auxiliary liquid reservoir has an auxiliary variable volume expandable only after the threshold volume is exceeded up to a maximum volume.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic of a liquid cooling system having a liquid load, a pump and reservoir package and an auxiliary reservoir of the present invention.

FIG. 2 shows a diagrammatic illustration of the pump and reservoir package and the auxiliary reservoir of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 shows a schematic of liquid system 10 having pump package 12, liquid loads 14, 16 and 18, and auxiliary reservoir 20. Pump package 12 includes pump 22, primary reservoir 24 and valve 26. Liquid loads 14 and 16 include heat exchangers 28 and 30, respectively, and liquid load 14 includes check valve 32 and diverter valve 34. Liquid load 18 includes cooling circuits 36A and 36B (which include evaporators 38A and 38B and condensers 40A and 40B, respectively), pressure sensor 42 and temperature sensor 44. Liquid loads 14, 16 and 18 and auxiliary reservoir 20 are connected to pump package 12 with liquid lines 46A-46F.

Liquid system 10 comprises a system for circulating fluid through a closed circulation loop. For example, system 10 may comprise a cooling system integrated into an aircraft environmental control system (ECS) that circulates a cooling fluid. As such, system 10 is typically incorporated into an aircraft airframe. Liquid loads 14, 16 and 18 represent areas or spaces within the airframe that demand different levels and types of cooling. For example, liquid load 18 comprises a pressurized cargo bay portion of the airframe where aircraft electronics, such as power electronics or avionics, are stored. Liquid loads 14 and 16 comprise unpressurized regions of the airframe such as pack bays where ECS equipment is stowed. However, any space within an aircraft, such as the cabin, may be connected to system 10. Liquid system 10 provides a fluid medium that transfers heat to and from various places within system 10.

Pump 22 of pump package 12 pressurizes a cooling fluid within loop lines 46A-46F. The fluid flows from pump package 12 to liquid load 18 through line 46A. Cooling circuits 36A and 36B of liquid load 18 are in thermal communication with lines 46A and 46B through evaporators 38A and 38B, and with lines 48A and 48B through condensers 40A and 40B. Although two circuits are shown, additional circuits may be added as provided by design requirements. Cooling fluid in lines 48A and 48B is heated by circulating through hot electronics (or heat exchangers in thermal communication with the electronics) and cooled by circulating through cooled heat exchangers in communication with ram air ducts (not shown). Evaporators 38A and 38B unload heat from system 10 and condensers 40A and 40B impart the heat into lines 48A and 48B for removal from circuits 36A and 36B by the ram air ducts. Thus, the fluid of system 10 is cooled by circuits 36A and 36B before flowing into liquid loads 14 and 16 through line 46C.

The pack bays of liquid loads 14 and 16 contain environmental control systems that provide conditioned air to passenger areas of the aircraft cabin. Fluid line 46E connects liquid load 16 in parallel with liquid load 14. The chilled cooling fluid of system 10 absorbs heat from heat exchangers 28 and 30, through which a separate fluid flows in lines 50 and 52, respectively. Liquid system 10 may include other systems that dump heat to or take heat from fluid of lines 46A-46D either directly or through conduction. For example, system 10 may be linked to galley cooling systems of the aircraft between liquid loads 18 and 14. Examples of various liquid loads used in conjunction with liquid circulation loops are described in U.S. Pat. No. 4,550,573, which is assigned to United Technologies Corporation, and U.S. Pat. Nos. 6,415,595 and 7,334,422, which are assigned to Hamilton Sundstrand Corporation, all of which are incorporated by reference. In exemplary embodiments, a liquid circulates through a closed loop system that transfers and removes heat from the system.

System 10 includes various other components, including valves and sensors, for maintaining operation of system 10. Valves 32 and 34 operate to bring liquid loads 14 and 16 into fluid communication with liquid system 10 properly. Diverter valve 34 can be closed to bypass loads 14 and 16 such as for safety, maintenance or performance issues. Check valve 32 prevents fluid within lines 46A-46E from flowing backwards through system 10. Relief valve 26, which may be placed anywhere along fluid lines 46A-46D, allows fluid to escape from line 46D when pressure within system 10 exceeds a maximum pressure. Pressure sensor 42 and temperature sensor 44 provide input signals to an aircraft controller to monitor the performance of system 10. For example, the speed of pump 22 can be adjusted based on the pressures and temperatures of system 10. Also, sensors 42 and 44 allow calculations to be performed to determine fluid levels in system 10.

Reservoir 24 comprises a variable enclosed volume that allows the fluid within system 10 to expand. For example, cooling fluid within system 10 retains heat from liquid loads 14-18, which thermally expands the fluid. Furthermore, ambient heat from atmospheric conditions expands the volume of the fluid within system 10. The thermal expansion of the fluid exceeds the total system volume provided by lines 46A-46F and pump 22. Specifically, system 10 operates optimally when fluid fills the system and air is omitted from the system. Thus, when the fluid expands, reservoir 24 provides extra system volume that adjusts so system 10 is always operating optimally. Without a reservoir, thermal expansion of the fluid would increase the pressure of system 10 to operate valve 26. Fluid would thus be expelled from system 10 as valve 26 opens at the maximum pressure. However, the expelled fluid would be lost such that upon a reduction in the temperature of the fluid, system 10 would not be full and would be operating below optimum conditions. Reservoir 24 thus allows system 10 to operate optimally during widely varying ranges of conditions. Thus, the capacity of reservoir 24 is closely matched to the expected operating conditions of system 10 and the particular liquid loads to which system 10 is connected.

It is sometimes desirable to change the configuration of system 10. For example, more cooling loops, similar to circuits 36A and 36B, may be added to liquid load 18. These loads may require system 10 to carry a greater volume of cooling fluid, as might be needed for greater lengths of fluid lines or for increases in cooling performance. Additionally, the configuration of system 10 may change as system 10 is incorporated into a different aircraft airframe. It is, however, desirable to maintain system 10 as close as possible to original design specifications to avoid the need to have to recertify existing components to performance and safety specifications. In particular, it is difficult to redesign pump package 12 because pump 22 and reservoir 24 are incorporated into a single housing, as is described in more detail with reference to FIG. 2. Thus, it is not possible to simply expand the capacity of reservoir 24 without redesigning pump package 12. Auxiliary reservoir 20 of the present invention provides system 10 with additional volumetric capacity beyond what is provided by reservoir 24. Auxiliary reservoir 20 can be linked into system 10 along any portion of lines 46A-46E. Thus, system 10 can be reconfigured and repackaged for easy incorporation into other airframes. Furthermore, the construction of pump package 12 need not be disturbed to do so. Auxiliary reservoir 20 is also designed to not disturb the performance of reservoir 24 until auxiliary capacity is needed, as is described with reference to FIG. 2.

FIG. 2 shows a diagrammatic illustration of pump package 12, separate auxiliary reservoir 20, pump 22, primary reservoir 24, liquid load 14 and valve 26. Auxiliary reservoir 20 includes housing 54, bellows 56, spring 58 and cap 60. Pump package 12 includes housing 62, reservoir cylinder 64, piston 66, inlet chamber 68, outlet chamber 70 and level sensor 71. FIG. 2 is shown to illustrate the present invention including the various volumes within each component and is not shown to scale.

Low pressure system fluid F_(LP) enters liquid load 14 through fluid line 46C after having passed through liquid load 18 (FIG. 1). Within liquid load 14, F_(LP) is in thermal communication with heat exchanger 28 (FIG. 1) whereby heat is absorbed into fluid F_(LP). After passing through liquid load 14, low pressure fluid F_(LP) is ready to be re-circulated through system 10 to continue the cycle of heat removal. Low pressure fluid F_(LP) flows from liquid load 14 to pump package 12 through liquid line 46D. Along the way to pump package 12, fluid F_(LP) passes valve 26 and auxiliary reservoir 20 and exerts pressure on valve 26 and reservoir 20 commensurate with system pressure at that point. As discussed below, valve 26 and reservoir 20 open at specific pressures to ensure functionality of system 10. As shown in FIG. 2, auxiliary reservoir 20 is shown in an evacuated state where no fluid is stored.

At pump package 12, low pressure fluid F_(LP) enters inlet chamber 68 within housing 62. Specifically, low pressure fluid F_(LP) enters cylinder 64 where piston 66 exerts atmospheric pressure P_(A) on chamber 68. The lowest pressure within system 10 occurs at inlet chamber 68. As pressure within system 10 rises due to increased temperature of fluid F_(LP), fluid within inlet chamber 68 exerts a force on piston 66. Fluid continues into pump 22 from chamber 68. Within pump 22, the fluid becomes pressurized using any conventional compression means. For example, pump 22 may comprise rotary vane pump or a centrifugal pump. Furthermore, pump 22 may comprise a tandem pump unit for reasons of redundancy and safety.

Fluid pressurized within pump 22 is discharged into outlet chamber 70. High pressure fluid F_(HP) exerts a force on piston 66 such that pressurization of reservoir 24 is provided by operation of pump 22. Thus, primary reservoir 24 comprises a bootstrap reservoir as is known in the art. For example, U.S. Pat. No. 4,691,739 to Gooden describes a typical bootstrap reservoir configuration. Although described with respect to an integrated pump and bootstrap-charged reservoir, any pump reservoir combination may be used. For example, an integrated pump and gas-charged reservoir is described in U.S. Pat. No. 4,906,166, which is assigned to Sundstrand Corporation. In yet other embodiments, pump 22 and primary reservoir 24 are not integrated. In any embodiment, the highest pressure in system 10 occurs at the outlet of pump 22, which is outlet chamber 70 for the described embodiment. From outlet chamber 70, high pressure fluid F_(HP) leaves reservoir 24 and enters fluid line 46A for circulation through system 10 and returning to liquid load 14 as low pressure fluid F_(LP).

As heat accumulates in low pressure fluid F_(LP) due to system operation and increases in ambient temperature, the volume of F_(LP) increases. System 10 is designed to operate fully charged, i.e. with no empty space in lines 46A-46E or pump 22. As such, volumetric expansion of F_(LP) due to temperature increases causes the pressure within system 10 to increase. Primary reservoir 24 and auxiliary reservoir 20 provide extra volumetric capacity to system 10 to accommodate thermal expansion of fluid F_(LP). In particular, primary reservoir 24 and auxiliary reservoir 20 provide active or real-time increases in system capacity so that system 10 is always fully charged. Furthermore, activation of primary reservoir 24 and auxiliary reservoir 20 is staged such that utilization of the volumetric capacity of auxiliary reservoir 20 occurs only after the volumetric capacity of primary reservoir 24 is maxed out.

As pressure within system 10 rises, pressure within inlet chamber 68 rises, overcoming atmospheric pressure P_(A) and pressure of high pressure fluid F_(HP) on piston 66. Piston 66 thus rises (as shown in FIG. 2) within cylinder 64 such that more space within cylinder 64 is allocated to inlet chamber 68 and less space is allocated to outlet chamber 70. Level sensor 71 provides input to a system controller that indicates the position of piston 55 and/or the liquid level in cylinder 64. The input can be referenced with pressure and temperature data sensed by pressure sensor 42 and temperature sensor 44 (FIG. 1) to verify operation of system 10. However, piston 66 can only traverse cylinder 64 until piston flange 72 engages cylinder stops 74. At such point, the volumetric capacity of primary reservoir 24 becomes maxed out, or reaches a threshold level where utilization of auxiliary reservoir 20 is initiated. Thus, primary reservoir 24 has an operating range extending from the minimum operating pressure of system 10 to a pressure below the maximum operating pressure of system 10. Upon initiation of system 10, pressure at inlet chamber 68 will rise to the minimum system operating pressure. Atmospheric pressure P_(A) and the pressure of high pressure fluid F_(HP) will maintain piston 66 in a collapsed or fully downward position within cylinder 64, insofar as the liquid level in the primary reservoir 24 will allow. As system 10 increases operating temperature above the minimum due to operating or ambient conditions, piston 66 rises until the threshold pressure is reached.

Auxiliary reservoir 20 comprises a spring-charged reservoir in which spring 58 biases the position of cap 60 against housing 54. Spring 58 maintains the volumetric capacity within housing 54, the space between cap 60 and fluid line 46F, closed until the threshold pressure is reached. Spring 58 pushes downward on cap 60 such that low pressure fluid F_(LP) is not able to enter housing 54 through line 46F. Spring 58 has a spring force set to yield at or above the threshold pressure of primary reservoir 24. Thus, spring 58 will not allow cap 60 to move, making the volumetric capacity within housing 54 unavailable, until the threshold level is exceeded and the volumetric capacity of primary reservoir 24 is full. As auxiliary reservoir 20 fills with fluid, bellows 56 expands and cap 60 rises within housing 54. Bellows 56 comprises a flexible metal sleeve that hermetically seals low pressure fluid F_(LP) within housing 54, preventing the fluid from moving to the back side of cap 60. Cap 60 can continue to retreat until spring 58 is fully compressed. At such point, system 10 reaches its maximum volumetric capacity, as both primary reservoir 24 and auxiliary reservoir 20 are full. After reservoirs 20 and 24 fill up, any further increase in volume of low pressure fluid F_(LP) will cause valve 26 to release fluid from system 10. Valve 26 may comprise any pressure relief valve as is know in the art. System 10 returns to lower operating pressures in reverse order, with auxiliary reservoir 20 emptying completely before primary reservoir 24 reduces fluid volume. Spring 58 ensures that any fluid within housing 54 is recharged into lines 46A-46F for circulation through the system 10.

In other embodiments, auxiliary reservoir 20 may comprise a gas-charged reservoir where the back side of cap 60 within housing 54 is charged with a compressible gas that acts as a spring force. Auxiliary reservoir 20 may also be provided with additional features such as de-aeration and bleed ports, level sensors, temperature sensors and pressure sensors. However, auxiliary reservoir 20 need not have a dedicated level sensor so long as reservoir 24 is provided with level sensor 71. For example, auxiliary reservoir 20 can be sized to provide volume for the extreme upper limit of the operating pressure range of system 10. Thus, auxiliary reservoir 20 need only be engaged by system 10 a small amount of time. When level sensor 71 indicates primary reservoir 24 is at full capacity, a system controller will be able to determine that auxiliary reservoir 20 went into use. After returning to pressures within the operating range of primary reservoir 24, the system controller can verify fluid levels in system 10 by rechecking data from level sensor 71, pressure sensor 42 and temperature sensor 44. If fluid levels are indicated as being low, the controller can determine that pressures within system 10 exceeded the maximum pressure such that valve 26 was activated and fluid was lost. Thus, a system operator can be alerted by the controller to the fact that system 10 may need maintenance.

Auxiliary reservoir 20 increases the volumetric fluid capacity of system 10 without interfering with the installation or operation of system 10 and pump package 12. Auxiliary reservoir 20 can be spliced into fluid line 46D at any position. Any space within an airframe available may be used to accommodate auxiliary reservoir 20. Thus, the addition of additional cooling demands, such as an additional cooling circuit being connected to liquid load 18, can be easily accommodated. Furthermore, the packaging of pump 22 and 24 need not be disturbed to increase capacity of system 10. System 10, including auxiliary reservoir 20, can be filled by simply filling system 10 with fluid until valve 26 releases fluid such that all air is purged from system 10, as would be done without auxiliary reservoir 20. The timing of the activation of auxiliary reservoir 20 allows pump package 12 to function as if auxiliary reservoir 20 were not part of the system when operating below the threshold level. Thus, the pumping performance of pump 22 will remain unaffected below the threshold level.

While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims. 

1. A liquid system for circulating a liquid through a circulation loop, the liquid system comprising: a liquid pump for pressurizing liquid within the circulation loop; a primary liquid reservoir in fluid communication with the circulation loop and having a primary variable volume expandable to accommodate volumetric expansion of pressurized liquid up to a threshold volume; and an auxiliary liquid reservoir in fluid communication with the circulation loop and having an auxiliary variable volume expandable only after the threshold volume is exceeded up to a maximum volume.
 2. The liquid system of claim 1 wherein the primary variable volume accommodates volumetric expansion of the liquid across operating pressures of the liquid pump up to a threshold pressure.
 3. The liquid system of claim 2 wherein the auxiliary variable volume accommodates volumetric expansion of the liquid above the threshold pressure up to a maximum pressure.
 4. The liquid system of claim 3 and further comprising: a relief valve connected to the circulation loop and configured to open above the maximum pressure.
 5. The liquid system of claim 3 wherein the auxiliary liquid reservoir comprises a spring-charged bellows having a spring with a spring force that yields above the threshold pressure.
 6. The liquid system of claim 5 wherein the primary liquid reservoir comprises a bootstrap reservoir.
 7. The liquid system of claim 6 wherein the liquid pump and the primary liquid reservoir are packaged in a common housing and the auxiliary liquid reservoir is packaged in a separate housing.
 8. The liquid system of claim 6 wherein the primary liquid reservoir includes a level sensor for determining a volume of fluid within the primary liquid reservoir.
 9. The liquid system of claim 1 and further comprising: a liquid circulating through the circulation loop; and a liquid load connected to the liquid pump through the circulation loop; wherein the liquid load imparts a thermal input to the liquid.
 10. A liquid system comprising: a circulation loop; a fluid pump configured to pressurize fluid within the circulation loop; a primary reservoir in fluid communication with the circulation loop and configured to expand in volume under pressure within the circulation loop up to a threshold pressure; and an auxiliary reservoir in fluid communication with the circulation loop and configured to expand in volume once the threshold pressure is exceeded.
 11. The liquid system of claim 10 and further comprising: a liquid circulating through the circulation loop; and a liquid load connected to the liquid pump through the circulation loop; wherein the liquid load imparts a thermal input to the liquid.
 12. The liquid system of claim 11 wherein the auxiliary reservoir comprises a spring charged bellows having a spring with a spring force that yields above the threshold pressure.
 13. The liquid system of claim 12 wherein the primary reservoir comprises a bootstrap reservoir integrated into a housing of the fluid pump, and the auxiliary reservoir is packaged in a separate housing.
 14. The liquid system of claim 12 wherein the primary reservoir includes a level sensor for determining a volume of fluid within the primary reservoir.
 15. The liquid system of claim 10 wherein the auxiliary reservoir expands to a maximum volume after the primary reservoir expands to a threshold volume.
 16. A method of accommodating expanding fluid in a closed fluid circulation loop, the method comprising: circulating pressurized fluid in a closed fluid circulation loop using a pump; expanding a volume of a primary reservoir connected to the closed fluid circulation loop up to a threshold volume to accommodate expansion of the pressurized fluid to a threshold level; and expanding a volume of an auxiliary reservoir connected to the closed fluid circulation loop up to a maximum volume to accommodate expansion of the pressurized fluid from the threshold level to a maximum level.
 17. The method of claim 16 wherein the volume of the primary reservoir and the volume of the auxiliary reservoir are expanded sequentially.
 18. The method of claim 16 wherein the volume of the primary reservoir is expanded to a threshold pressure and the volume of the auxiliary reservoir is expended after the threshold pressure is reached.
 19. The method of claim 18 wherein the step of expanding the volume of the primary reservoir comprises expanding a bootstrap reservoir integrated with the pump.
 20. The method of claim 19 wherein the step of expanding the volume of the auxiliary reservoir comprises expanding a bellow-type reservoir having a spring that yields at the threshold pressure. 